Corruptly merge constants with explicit and implicit alignments.

Constant merge can merge a constant with implicit alignment with one that has
explicit alignment. Before this change it was assuming that the explicit
alignment was higher than the implicit one, causing the result to be under
aligned in some cases.

Fixes pr17815.

Patch by Chris Smowton!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194506 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 4 deletions

diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp
index a7bf188..d94c0f4 100644
--- a/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/lib/Transforms/IPO/ConstantMerge.cpp
@@ -93,9 +93,12 @@ bool ConstantMerge::hasKnownAlignment(GlobalVariable *GV) const {
 }
 
 unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const {
+  unsigned Align = GV->getAlignment();
+  if (Align)
+    return Align;
   if (TD)
     return TD->getPreferredAlignment(GV);
-  return GV->getAlignment();
+  return 0;
 }
 
 bool ConstantMerge::runOnModule(Module &M) {
@@ -210,9 +213,9 @@ bool ConstantMerge::runOnModule(Module &M) {
       // Bump the alignment if necessary.
       if (Replacements[i].first->getAlignment() ||
           Replacements[i].second->getAlignment()) {
-        Replacements[i].second->setAlignment(std::max(
-            Replacements[i].first->getAlignment(),
-            Replacements[i].second->getAlignment()));
+        Replacements[i].second->setAlignment(
+            std::max(getAlignment(Replacements[i].first),
+                     getAlignment(Replacements[i].second)));
       }
 
       // Eliminate any uses of the dead global.